The death last fall of a 17-year-old patient at the University of Pennsylvania Medical Center shocked the medical research community. The young man, who suffered from a rare genetic defect that stopped his body from metabolizing ammonia, was undergoing an experimental form of treatment called gene therapy. In theory at least, it should be possible to treat a number of devastating diseases by patching in bits of DNA to repair defective or missing genes.

In practice, gene therapy remains difficult and the methods crude. One problem is in sneaking the new genetic material into the cell and getting it incorporated into existing DNA without the individual’s immune system going berserk. Most approaches rely on nature’s masterful Trojan Horse, the virus. In the case of the patient at Penn, researchers injected very high doses of a modified form of the common cold virus directly into his liver. Once inside, the viral particles were supposed to insert replacement DNA into tissue cells so his liver could start to process ammonia normally. Four days later the patient was dead from multiple organ failure, and speculation centered on the possibility that the immense and sudden injection of the virus caused an overwhelming immune response.

Medical researchers have been terrified of just this scenario since human gene therapy experiments began a decade ago. Now that it’s happened, their motivation to find safer alternatives for delivering genes to human cells has been redoubled. Enter nanotechnology. The fabrication of objects and devices on the scale of nanometers has been making rapid progress in the physical sciences. But you wouldn’t necessarily think of it in connection with medicine. Yet nanotechniques might offer a solution to current problems in gene therapy-and some remarkable advantages in treating stubborn diseases such as cancer and diabetes.

A small vanguard of medical explorers is exploiting the tools of nanotechnology to manipulate biomolecules that regulate life and death, illness and health. The key to these efforts is that researchers are learning how to tailor devices and materials on the scale of billionths of a meter, thereby acquiring the ability to engineer structures and machines no bigger than biomolecules such as DNA. They’re finally playing on the size scale of biology itself. And that means they may be able to design tiny tools to safely and effectively fix the nanoscopic machinery of illness, just as a mechanic works on a car’s engine using tools that are on the same scale as the engine. This may sound like science fiction-and until recently it was-but it’s reaching the verge of possibility because teams of doctors and scientists are combining advances from biology and chemistry with the synthesis and fabrication tools from chemical engineering, even the microchip industry.